The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 199 51 038.5, filed on Oct. 22, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a roll, e.g., for smoothing paper webs, that includes a hard roll core made of, e.g., metal and an elastic layer provided on an outside of the hard roll. The covering layer includes a radially outer functional layer and a radially inner connecting layer arranged to connect the functional layer to the roll core.
2. Discussion of Background Information
Elastic rolls of this kind are used, e.g., in the satining of paper webs. Here, one elastic roll forms, in each case together with a hard roll, a press gap through which the paper web to be treated is guided. While the hard roll has a very smooth surface made of, e.g., steel or chilled cast iron and is responsible for the smoothing of the side of paper web facing it, the elastic roll acts on the opposite side of the paper web to effect a homogenizing and compacting of the paper web in the nip. The order of magnitude of the rolls ranges from lengths of about 3-12 m and diameters from about 450-1500 mm. They can withstand line forces of up to about 600 N/mm and compressive stresses of up to about 130 N/mm2.
As the trend in paper manufacturing is toward performing satining in an online operation, i.e., toward guiding the paper web exiting the paper machine or coating machine directly through the paper smoothing apparatus (calender), higher demands than previously are made on the rolls of the smoothing apparatus, particularly with respect to temperature resistance. As a result of the high transportation speeds of the paper web required in online operation and the high rotation speeds of the calender rolls associated with this, the nip frequency, i.e., the frequency with which the covering is compressed and relieved of its load again, is increased, which in turn leads to increased roll temperatures. These high temperatures arising in online operation lead to problems which can even lead to the destruction of the plastic coatings in known elastic rolls. With known plastic coatings, maximum temperature differences of around 20xc2x0 C. are permissible over the width of the roll and, the plastics conventionally used for the coating have a substantially higher coefficient of thermal expansion than the conventionally used steel rolls or chilled cast-iron rolls so that high axial stresses occur between the steel roll or the chilled cast-iron roll and the plastic coating associated with it due to an increase in temperature.
So-called hot spots, at which a peeling or even a breaking open of the plastic layer occurs, arise dine to these high stresses in conjunction with hot regions occurring particularly in spot form.
These hot spots can occur when, in addition to the mechanical stresses and the relatively high temperature, crystallization spots exist in the form of, e.g., defective adhesive bonds, deposits or above-average recesses in the elastic coating, e.g., due to creases or foreign bodies on the paper web. In these cases, the temperature to the crystallization spots can increase from the normal about 80xc2x0 C.-90xc2x0 C. to more than about 150xc2x0 C., due to which the above-mentioned destruction of the plastic layer occurs.
To achieve a high service life of the elastic rolls, it must be ensured that the covering layer is not destroyed by either its internal heating, which occurs in operation, or by high local mechanical excessive stresses, which occur in operation.
The present invention provides a roll of the kind generally mentioned above, in which the risk of the occurrence of hot spots is reduced and high local excessive stresses will also not lead to the destruction of the elastic covering layer.
Accordingly, the present invention includes a roll, similar in general to that mentioned above, in which the inner connecting layer and the outer functional layer each include a soft matrix material with fibers embedded therein. The matrix material of the functional layer is a highly elastic material with a damping factor of tan xcex4 less than about 0.02 and the matrix material of the connecting layer is a highly damping material with a damping factor of tan xcex4 greater than about 0.05. The damping factor tan xcex4 is defined here by the equation tan xcex4=Exe2x80x2/Exe2x80x3, where E represents the modulus of elasticity with its real part Exe2x80x2 and its imaginary part Exe2x80x3.
In accordance with the invention, the covering layer is split into two partial layers, each of which is optimized for its respective task. While the local excessive stresses are taken up and damped by the highly damping matrix material in the connecting layer, so that the elastic roll is relatively insensitive to high local excessive stresses, the flexibility of the roll surface required for a high quality staining result and the low internal warming of the outer regions of the covering layer are ensured by the highly elastic material of the functional layer.
The matrix material preferably includes a plastic material, e.g., a thermosetting plastic or a thermoplastic. It must be pointed out here that the term xe2x80x9csoftxe2x80x9d when used in connection with the matrix material, is only to be understood in relation to the outer side of the metal roll, in particular the steel roll, termed as xe2x80x9chard.xe2x80x9d
The heat dissipation inside the connecting layer is increased and the desired stiffness of the connecting layer is achieved by the fibers embedded in the matrix material of the connecting layer. The same applies to the fibers embedded in the functional layer, such that the heat, which only occurs to a lower degree here due to the highly elastic matrix material, is dissipated essentially completely via the fibers.
In accordance with an advantageous embodiment of the invention, the fiber content of the connecting layer is approximately 40 to 70 vol. %, in particular approximately 50 to 60 vol. %. The fiber content of the functional layer, in contrast, is advantageously approximately 5 to 30 vol. %, in particular approximately 8 to 20 vol. %.
Since the connection layer should have a greater stiffness than the functional layer and, since a higher heat dissipation is required in the radially inner connecting layer, the connecting layer has a higher fiber content than the functional layer.
The connecting layer preferably has a greater radial thickness than the functional layer, with the radial thickness of the connecting layer advantageously being approximately 30 to 70%, in particular approximately 50%, greater than the radial thickness of the functional layer. Suitable values for the radial thickness of the connecting layer can be approximately 8 to 15 mm, preferably approximately 12 mm, and for the radial thickness of the functional layer approximately 5 to 12 mm, preferably approximately 8 mm.
The desired property of the connecting layer with respect to a high capability to take up large local excessive stresses is improved by its greater radial thickness since the large local excessive stresses are greatly damped by the relatively thick connecting layer.
In accordance with another preferred embodiment of the invention, the fibers of the functional layer and/or of the connecting layer have a higher thermal conductivity than the matrix material in which they are embedded. The fibers of the functional layer and/or the connective layer can be made of, e.g., carbon fibers and/or metal fibers.
In this way, it is achieved that the heat occurring inside the functional layer and/or the connecting layer is dissipated fast and safely before the heat occurring can lead to the destruction of the covering layer.
Further, fillers, whose thermal conductivity is, e.g., greater than the thermal conductivity of the matrix material in each case, can advantageously be present in the functional layer and/or connecting layer in addition to the fibers. The fillers can be made of, e.g., carbon and/or metal, preferably in powder or fiber form.
A further improvement in the thermal conductivity of the relevant matrix material is achieved by these fillers.
The present invention is directed to a roll for the smoothing paper webs. The roll includes a hard core, and an elastic covering layer arranged on an outside of the hard core. The covering layer includes a radially outer functional layer and a radially inner connecting layer arranged to couple the functional layer to the hard core. The inner connecting layer and the outer functional layer each include a soft matrix material with embedded fibers. The matrix material of the functional layer includes an elastic material with a damping factor of tan xcex4 less than about 0.02 and the matrix material of the connecting layer includes a damping material with a damping factor of tan xcex4 greater than about 0.05.
In accordance with a feature of the present invention, the hard core can include a metal core. Further, the metal core may include one of a steel and chilled cast iron core.
According to another feature of the invention, the matrix materials have a modulus of elasticity comprising real and imaginary components, and tan xcex4 represents the real component of the modulus of elasticity divided by the imaginary component of the modulus of elasticity.
The matrix material of at least one of the functional layer and the connecting layer may include plastic. The plastic may be one of a thermosetting plastic and a thermoplastic.
Further, the matrix material of at least one of the functional layer and the connecting layer can include a resin/hardener combination.
According to another feature of the invention, a fiber content of the connecting layer can be approximately 40-70 vol. %. The fiber content may be approximately 50-60 vol. %.
Moreover, a fiber content of the functional layer is approximately 5-30 vol. %, and the fiber content can be approximately 8-20 vol. %.
The connecting layer can have a radial thickness greater than a radial thickness of the functional layer. The radial thickness of the connecting layer may be approximately 30-70% greater than the radial thickness of the functional layer. Further, the radial thickness of the connecting layer can be approximately 50% greater than the radial thickness of the functional layer. Still further, the radial thickness of the connecting layer may be approximately 8-15 mm, and the radial thickness of the connecting layer can be approximately 12 mm. The radial thickness of the functional layer may be approximately 5-12 mm, and the radial thickness of the functional layer can be approximately 8 mm.
In accordance with another feature of the instant invention, the fibers of at least one of the functional layer and the connecting layer can have a thermal conductivity higher than a thermal conductivity of the matrix material into which the fibers are embedded.
According to still another feature of the present invention, the fibers of at least one of the functional layer and the connecting layer can include at least one of carbon fibers and metal fibers.
Moreover, fillers can be provided in at least one of the functional layer and the connecting layer. A thermal conductivity of the fillers may be greater than a thermal conductivity of the matrix material. The fillers can include at least one of carbon and metal.
In accordance with a further feature of the invention, fillers can be provided in the functional layer.
The functional layer may include a plurality of layers and the connecting layer can include a plurality of fiber layers.
The connecting layer may include between 10 and 90 fiber layers, and the connecting layer can include between 40 and 50 fiber layers.
The present invention is directed to a roll for the smoothing paper webs. The roll includes a hard c(ore and an elastic covering layer arranged on an outside of the hard core. The covering layer includes a radially outer functional layer and a radially inner connecting layer arranged to couple the functional layer to the hard core. The inner connecting layer includes a damping matrix material with embedded fibers arranged to damp local mechanical stresses, and the outer functional layer includes an elastic matrix material with embedded fibers arranged for satining the paper webs.
In accordance with yet another feature of the instant invention, the outer functional layer may further include fillers arranged to increase a thermal conductivity of the outer functional layer.
The present invention is directed to a process for producing a roll for smoothing paper webs, where the roll includes a hard core. The process includes forming an outer functional layer with an elastic matrix material having a damping factor of tan xcex4 less than about 0.02 and embedded fibers, forming an inner connecting layer with a damping matrix material having a damping factor of tan xcex4 greater than about 0.05 and embedded fibers, and coupling the outer functional layer to the hard core through the inner connecting layer to form an elastic covering layer on an outside of the hard core.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.